I used to love this game on 'Mock the Week'. Think of a scenario, then give an example of something that a person in that scenario would be very unlikely to say. Feel free to use a previously-used scenario, or come up with a new one if you prefer; either is good. For example:
Things you'd never hear in a Star Wars movie:
"Bugger the force Luke, just bung a rock at it!"
Things you'd never hear in a Star Wars movie:
"Bugger the force Luke, just bung a rock at it!"